Yes but they both target horizontial scale out and OLTP is a target for both.
And yes, cockroach isn’t Postgres but it has SQL, versus something like Mongo or Cassandra.
And yes, cockroach isn’t Postgres but it has SQL, versus something like Mongo or Cassandra.
Citus is best used when transactions don't cross shard boundaries, in which case they execute on a single node and give you the low-latency to match.
The part about 2PC still holds.
Spanner uses Paxos (consensus) for replication within a key range (shard), but two-phase commit across shards: https://ai.google/research/pubs/pub39966
Citus relies on PostgreSQL's streaming replication, which gives higher throughput than Paxos, but Paxos has better availability characteristics. On the other hand, Paxos with leader leases as used by Spanner is similar to streaming replication both in terms of performance characteristics and short downtime during failover.